International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp. 445–450, Article ID: IJCIET_10_04_048
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJCIET&VType=10&IType=4
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
Scopus Indexed
STUDY OF MOISTURE DIFFUSION IN
CELLULAR CONSTRUCTIONAL MATERIALS
Gladkov Alexander Alekseevich, Chastnikov Arseniy Aleksandrovich, Arutyunyan
Arman Ashotovich, Turov Aleksandr Vadimovich, Gaidar Nikita Sergeevich,
Zelentsov Aleksandr Aleksandrovich, Zakharov Oleg Andreevich
Moscow State University of Civil Engineering (MGSU) National Research University,
26, Yaroslavskoye Shosse, Moscow, Russia
ABSTRACT
The article presents the results of studies of the kinetics of changes in the diffusion
coefficients of moisture in wet cellular materials of enclosing structures of buildings,
in relation to the moisture content. The presented method makes it possible to obtain
the diffusion coefficients of moisture in the cellular materials in the entire range of
moisture from a single experiment, which naturally lasts about 2-3 days.
This makes it possible to solve the tasks of the heat and humidity regime of
homogeneous enclosing structures of buildings according to equation (2), similar to
the Fourier equation based on the moisture content gradient. It is necessary for
multilayer structures to have boundary conditions of type IV, i.e., respectively,
equilibrium moisture content at the joints of materials.
Key words: moisture diffusion coefficient, moisture conductivity of the cellular
constructional materials, vapor permeability of constructional materials.
Cite this Article: Gladkov Alexander Alekseevich, Chastnikov Arseniy
Aleksandrovich, Arutyunyan Arman Ashotovich, Turov Aleksandr Vadimovich,
Gaidar Nikita Sergeevich, Zelentsov Aleksandr Aleksandrovich, Zakharov Oleg
Andreevich, Study of Moisture Diffusion in Cellular Constructional Materials,
International Journal of Civil Engineering and Technology 10(4), 2019, pp. 445–450.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=4
1. INTRODUCTION
With the introduction of new heat-insulating materials with improved insulating properties the
thickness of the enclosing structures has decreased. In this regard, the concentration of
moisture per unit volume of material, which has a significant impact on the performance
properties of materials, has increased.
One of the problems in predicting the heat-moisture regime is the difficulty of obtaining
the diffusion coefficient of moisture. The most common method for calculating the moisture
state of external enclosing structures of building is to represent the flow of moisture in the
form of two components: the flow of vaporous moisture and the flow of liquid moisture.
http://www.iaeme.com/IJCIET/index.asp
445
editor@iaeme.com
Gladkov Alexander Alekseevich, Chastnikov Arseniy Aleksandrovich, Arutyunyan Arman Ashotovich,
Turov Aleksandr Vadimovich, Gaidar Nikita Sergeevich, Zelentsov Aleksandr Aleksandrovich,
Zakharov Oleg Andreevich
(1)
where μ is the vapor permeability coefficient (water vapor diffusion);
∇e is the gradient of the partial vapor pressure;
β is the moisture conductivity coefficient (diffusion of liquid moisture);
∇ω is the gradient of the liquid phase of moisture.
At the same time the vapor permeability coefficient of the cellular material is determined
according to GOST 25898-83 “Building materials and products. Methods for determining the
resistance to the vapor permeability” (Moscow: NIISF, 1983. P. 7) and the coefficient of
moisture conduction is determined by the methods given in the study [1].
The limit between the diffusion of vapor and liquid moisture is considered to be the
maximum sorption moisture content of materials (equilibrium ω, at ϕ = 98%).
However, this boundary is very conditional, since the liquid phase of moisture in the pores
of materials is formed with the onset of capillary condensation, which occurs for many porous
constructional materials much earlier than the maximum sorption (at φ = 70 ... 80%).
From the point of view of exploitation of external enclosing structures made of cellular
materials it does not matter how much water vapor has passed through the structure. It is
important how much liquid phase moisture is formed and remains in the structure.
From this point of view, the flow of moisture through the structure can be written as
follows:
(2)
where a (ω0) ω is the diffusion coefficient of moisture in a wide range of moisture content
of the material; ∇ω0 is the gradient of volume humidity. In this case, the diffusion coefficient
of moisture is a function of moisture content, i.e., a = f ω (ω0).
In the study [2], the technique for obtaining such a dependence is offered. The essence of
the method is as follows:
1. Make a square sample for testing with a thickness of 10 ... 20 mm and a width of 70 ... 100
mm.
2. The side surfaces of the sample are pre-waterproofed (Pic. 1).
Figure 1. Samples of cellular constructional materials with waterproofed side surfaces
http://www.iaeme.com/IJCIET/index.asp
446
editor@iaeme.com
Study of Moisture Diffusion in Cellular Constructional Materials
3. The evacuated sample is saturated with the degassed distilled water.
4. The sample is dried under normal conditions and the changes in weight has been recorded
over time until it is fully stabilized.
Thus, we obtain the drying material curve from the full saturation of the sample wmax to
the equilibrium moisture content with the environment wS (Fig. 2).
Figure 2. Curves of drying material: 1 - cement-sand mortar; 2 - claydite; 3 - foamed concrete
The relationship between the average moisture content wv (t) of the central layer R1 (Pic.
3) and the average moisture content wp(t) of the surface layer 1 (R – R1) can be found from
the average moisture content w0 (t) of the sample:
(3)
From the formula (3) we determine the values of moisture content: the surface layer for
the period of surface drying
(4)
the inner layer for the period of deep drying
(5)
The transition from surface to deep drying occurs at
while 1 R = R / 2.
Here wsat is the humidity at the saturated state of the sample; wrel is the equilibrium
moisture content of the sample, corresponding to the relative humidity of the environment.
http://www.iaeme.com/IJCIET/index.asp
447
editor@iaeme.com
Gladkov Alexander Alekseevich, Chastnikov Arseniy Aleksandrovich, Arutyunyan Arman Ashotovich,
Turov Aleksandr Vadimovich, Gaidar Nikita Sergeevich, Zelentsov Aleksandr Aleksandrovich,
Zakharov Oleg Andreevich
Figure 3. Scheme of changes in moisture content in the sample during double-sided drying: Surface
drying period
Figure 4. Scheme of changes in moisture content in the sample during double-sided drying: Deep
drying
After taking into account the readings of the experiment, it becomes possible to calculate
the diffusion coefficient at any relative humidity of the sample using the formula obtained in
the study [2]
http://www.iaeme.com/IJCIET/index.asp
448
editor@iaeme.com
Study of Moisture Diffusion in Cellular Constructional Materials
(6)
The approximation of drying graphs was carried out by the method of least squares. Next,
according to formula (6) the diffusion coefficient of moisture is calculated depending on the
humidity w0 and the corresponding graph of am (w0) is plotted.
The results of the experiment are shown in Pic.5 for three most typical construction
materials.
Figure 5. The change in the diffusion coefficient of moisture: 1 - cement-sand mortar; 2 - claydite; 3 foamed concrete
From Pic.4 it follows that the decrease in the diffusion coefficient in the initial section at
w0 = 0 is connected to the gradual blocking of through pores with liquid sorption moisture.
Most likely, the smooth horizontal section corresponds to the film-type movement of the
liquid phase of moisture. A further increase in the diffusion coefficients of moisture is
associated with the onset of volumetric motion of the liquid phase until the pores are
completely saturated.
CONCLUSIONS
Analyzing the results, we can make the following conclusions.
The presented method makes it possible to obtain the diffusion coefficients of moisture in
cellular materials in the entire range of moisture from a single experiment, which naturally
lasts about 2-3 days.
This makes it possible to solve the tasks of the heat and humidity regime of homogeneous
enclosing structures of buildings according to equation (2), similar to the Fourier equation
based on the moisture content gradient. It is necessary for multilayer structures to have
boundary conditions of type IV, i.e., respectively, equilibrium moisture content at the joints of
materials.
http://www.iaeme.com/IJCIET/index.asp
449
editor@iaeme.com
Gladkov Alexander Alekseevich, Chastnikov Arseniy Aleksandrovich, Arutyunyan Arman Ashotovich,
Turov Aleksandr Vadimovich, Gaidar Nikita Sergeevich, Zelentsov Aleksandr Aleksandrovich,
Zakharov Oleg Andreevich
REFERENCES
[1]
Fokin K.F. Construction heat engineering of the enclosing parts of buildings. M., 2018.
pp. 166–237.
[2]
Perehozhentsev A. G. Theoretical foundations and methods for calculating the
temperature-humidity regime of the enclosing parts of building. Volgograd: VolgGASU,
2018. pp. 72-78.
[3]
Avrorin, AV. Ecological house-building: [questions on the formation of energy-saving
policies in housing construction] / AV Avrorin [and others] // Problems of energy saving.
Ecology. - 1997. - No. 43. - P. 1-71.
[4]
Belkin, A. N. Ekodom: energy efficiency and environmental friendliness: [advanced
foreign experience in implementing energy efficient systems and technologies in
construction] / AN Belkin, IN Goltsov, EV Filippov // Housing construction. - 2011. - No.
7. - P. 41-43.
[5]
Voronin, AA Urban lodging: the multifaceted nature of environmental issues: [the
problems of building a mass lodging in accordance with the environmental requirements
of the time] / AA Voronin, BM Merzhanov // Housing construction. - 2005. - No. 1. - P.
10-11.
[6]
Dmitriev, V. Energy Efficiency and Ecology in Housing Construction // Building: New
Technologies, New Equipment. - 2007. - No. 4. - P. 57-60.
[7]
Zhigulina, A. Yu. Energy-efficient residential buildings. World and domestic practice of
design and construction: [the main design principles, methods for their implementation
and cost indicators of energy-efficient residential houses abroad and in Russia] // Urban
Development. - 2012. - No. 2. - P. 84-86.
[8]
Klyueva, TG Methodical bases of an estimation of investment appeal of ecological
housing construction / TGKluyeva // Intellect. Innovation. Investments. - 2010. - No. 2. P. 44-49.
[9]
Kokodeeva, NE Standards of durable construction: [ecological construction] / NE
Kokodeeva [and others] // Housing construction. - 2012. - No. 1. - P. 14-18.
[10]
Larionov, AN Modern trends in the development of ecological housing construction / AN
Larionov, Yu. V. Ivanova // Economic revival of Russia. - 2008. - No. 2. - P. 10-17.
http://www.iaeme.com/IJCIET/index.asp
450
editor@iaeme.com